Oftentimes a patient will require a continuous oxygen supply while at a medical facility or while at home under medical care. Oxygen delivery devices, such as the cannula, are well known in the medical arts. The typical means and method for attaching an oxygen supply cannula to a patient's nostrils involves attaching a pair of oxygen supply lines to the cannula and inserting the appropriate portions of the cannula into the patient's nostrils. Next, the oxygen supply lines are wrapped around the patient's ears and the remaining portions of the oxygen supply lines are left to hang below the patient's chin, where an adapter couples the two oxygen supply lines into a single oxygen supply line. Additionally, below the chin of the patient, most systems use a slide connector to hold the two supply lines snugly against the patient's neck.
The problems with the prior art arrangement are many and significant. First, the reason that the oxygen supply lines are wrapped around the patient's ears is to provide a support for the oxygen supply lines, as well as for the cannula attached thereto. Thus, in order to have the cannula smartly fitted into the patient's nostrils, as desired, the oxygen supply lines are typically wrapped quite tightly about the patient's ears and this is very painful for the patient. In response, some patients use a cushion around portions of their ears in order to mitigate the pain associated with having the oxygen supply lines so tightly tethered to their ears. Additionally, the tubing across the face leaves an unsightly, deep and irritating impression that becomes semi-permanent so long as the oxygen therapy continues. These impressions in the face of the patient are cosmetically undesirable and, in some cases, the pressure exerted by the tubes against the upper cheeks tends to force the patient's eyes closed, thus interfering with clear vision and causing watering of the eyes.
Another serious problem associated with the typical cannula oxygen supply system described above and with other previous designs is that the weight of the cannula results in a tendency to fall out of the patient's nostrils. For some patients this is simply unacceptable. Thus, they wrap the oxygen supply lines around their ears extremely tightly and they snug the lower portions of the oxygen supply lines very firmly against the neck. Accordingly, continued contact of the cannula, especially at the philtrum and around the unprotected upper lip and cheek areas causes inflammation and irritation and ulcerous conditions may occur after a period of time. Not only does the wearer inadvertently move the cannula while sleeping as the head moves from side to side, but also when eating and/or talking, further movement occurs.
The central section of prior art cannulas is a straight horizontal form that contacts the wearer at a small point in the center of the nasalabidial area (FIG. 6A). The cannula can easily tilt to the side allowing the hollow tubular nasal extensions, or nares, to come out of the nostril, contact the nasal walls or direct gas against the wall, all of which are a common source of discomfort. The nares of prior art cannulas are curved when viewed from then side but are essentially parallel to each other looking from the front, as shown in FIG. 6A. The triangular shape of the nose causes the outer walls of the nostrils to slope inwards and the tips of the nares can contact the walls even if the cannula does not tip to the side. Gas is often directed against the nasal walls and dries the mucous tissues causing ulcerous sores. It is important for comfort that the cannula be positioned on the face in such a way that the nares are located in the nostril away from the walls and gas is directed into the open area of the pharynx.
The tips of the nares deflect hairs inside the nostrils causing an unpleasant sensation that is especially disconcerting to a patient not accustomed to wearing these devices. Oftentimes the patient removes the cannula thus eliminating the benefit of supplemental oxygen.
The tendency for cannulas to move, tilt or roll comes from a number of forces acting on the cannula. Gravity acts to make the cannula fall out but it can also cause it to roll out of the nostrils on cannulas with a high center of gravity. Most, if not all prior art cannulas have a high center of gravity due to the weight of the nares and half the body located above the support tubing attachment point.
The majority of the force acting to urge the cannula out of position comes from the very tubing whose job it is to support the cannula. Insufficient flexibility and “memory” of the PVC tubing cause forces acting on one end of the tubing to affect the cannula at the other end. Insufficient flexibility, or stiffness, increases the force needed to bend the tubing when the head or parts of the face are moved and the cannula reacts to these forces by lifting off the face or tilting to the side.
Memory is a term describing the tendency for the tubing to “take a set” or adopt a shape after a period of time. This can easily be seen when a coiled cannula is first removed from its package and resembles a spring. FIG. 10 illustrates the shape adopted by tubing 29 when the cannula is worn on the head and acts like a frame attempting to hold the cannula in a fixed position. However, when the head is turned the nose drags the cannula along. The various rubbing actions that occur with each movement cause red spots and irritation under the nose and on the ears.
The support tubing is made from PVC, or polyvinyl chloride with a hardness of about 80 to 85 durometer Shore A that gives it a relatively high stiffness in torsion that makes it difficult to twist at one end if the other end is held rigid. Prior art cannulas make use of this stiffness to prevent the top-heavy cannulas from rolling over. The far ends of both support tubes are held rigid by bonding them side-by-side to a common coupling then the cannula is rotated to a predetermined angle and the remaining ends of the support tubes are bonded to each side. If the predetermined angle is correctly set then the nares will properly direct gas flow into the nasal cavity and the stiffness of the tubing will prevent rotation of the cannula. Unfortunately the correct angle for comfort is a fairly narrow range and the predetermined angle is set by hand so a significant number of cannulas do not fit well. An integral tab in the cannula body is designed to rest against the lip to rotate the cannula back into position by twisting the tubing and this can be a source of irritation.
FIG. 8 is a depiction of a step in the manufacturing process of prior art cannulas where the nares of the cannula are set at angle F before the tubes 29 are bonded 28 to fork connector 5. FIG. 9 shows how the tubing supports the cannula with the nares pointed in the correct direction when worn on the face of an individual. FIG. 10 illustrates how forcing the nares to a different angle causes the tubing to twist. Upon removal of the force, the nares snap back to their original position.
FIG. 6A shows a common injection molded prior art cannula with an integral tab intended to bear against the lip to limit rotation if the tubing does not point the nares properly. The main body is a horizontal hollow tube with support tubing bonded to each open end. The important point to note is that the support tubes are bonded directly in line with the rotational axis of the cannula body. All cannulas of this style rely on tubing stiffness to control the pointing angle of the nares.
The reasons generally given for using tubing of a specific hardness is that it is needed to resist crushing as might happen when a person is sleeping with the tubing pressed between their face and a pillow and secondly, the tubing must be sufficiently hard to resist kinking when the head is moved about. In general, the role tubing stiffness plays in preventing rotation is not well known in the field and does not appear in literature or in patents.
The invention described in U.S. Pat. No. 4,106,505 (Salter) uses a different method to orient the nares. It has a main body that is tall and narrow so that tension from the tubing bends the thin section of the cannula body around the upper lip to form a U-shape when viewed from above. The nares project from the body in the tall or vertical direction then curve toward the nasal passages so they are always pointed properly. Although undesirable tension is required to bend the cannula body, this style of prior art cannula does not require torsional rigidity to orient the nares and, in fact, the torsional rigidity can actually interfere with proper pointing in cases where the tubing is bonded such that it tries to rotate the cannula at some other angle.
The main supply tubing is generally made from the same material as the support tubing and also causes a number of problems in prior art cannulas. Regular PVC used in prior art cannulas have poor low temperature flexibility and become very stiff outside in the winter and have even been known to snap in two. It also has poor compression set properties that give it memory. The coil shape that remains after the cannula is removed from the package looks and acts like a spring that tries to pull back when extended. The constant force prevents the tubing from laying or draping nicely. Due to the stiffness of the material, movements that should only affect a small section of tubing, instead, involve longer sections that increase the likelihood of catching or entangling on some object.
This same characteristic also causes the main supply tubing to form twisted loops that kink and block the flow of oxygen, particularly in longer lengths. In the home, oxygen users usually have a central source of oxygen and use a long hose to supply oxygen at some distance from the source. This can be an integral part of the cannula in lengths up to 35 feet but, in many cases, the long length of main supply tubing is detachable so it can be reused when the cannula is changed. A coupler is used to connect the two pieces together as shown in FIG. 11.
The coiled shape acquired in the package never goes away completely and when the tubing is stretched out across the floor there will be small periodic humps rising slightly above the floor. These humps increase the chance of the tubing becoming caught under foot or entangled and they are also the reason that it is so common for prior art tubing to form twisted loops that eventually cut off the oxygen supply. The humps raise the tubing off the floor enough to provide the leverage to roll the tubing when it is dragged sideways across carpeting and wind it up. At some point the tubing relieves the stored energy by spinning a section of tubing into a spiral twisted loop like the twisted pile of a carpet. Eventually the tubing becomes kinked at the apex of the loop where the tubing makes a u-turn and heads back. This blocks the flow of oxygen and even when the twists are removed, the site of the kink is a weak spot that tends to encourage future kinking. Various swivel connectors have been developed to prevent this problem but they cause problems themselves by becoming caught in doorjambs or on furniture legs as they are dragged along.
A number of patents have been issued that were intended to solve one or more of the problems just discussed. One of these, U.S. Pat. No. 5,509,409, describes a plate-like face guard intended to protect the face from developing grooves caused by the tubing. U.S. Pat. Nos. 4,699,139, 4,949,733 and 6,026,811 are inventions for tubing pads to protect the ears while U.S. Pat. No. 5,025,805 is a tubing pad that protects both the face and the ears. U.S. Pat. Nos. 5,636,630 and 4,753,233 route the tubing to avoid the ear. U.S. Pat. Nos. 6,328,038, 6,505,624, 4,808,160, 4,836,200, 4,915,104, 4,995,384, 4,422,456, 5,704,916, 4,156,426, 4,660,555, 4,406,283, 5,438,979, 4,739,757, 5,188,101 and 4,367,735 all describe various straps or supports to hold the cannula in position. U.S. Pat. Nos. 5,113,857 and 5,794,619 are for devices that clip to the columella to secure the cannula. U.S. Pat. No. 5,526,806 is for a cannula without nares to avoid irritation inside the nostrils. U.S. Pat. Nos. 4,875,718, 5,222,486, 5,284,134, 5,572,994 and 5,797,627 are for swivel connectors to prevent twisting of supply tubing.
Therefore, there exists a need to provide a means for reliably attaching an oxygen cannula to a patient's nostrils without forming grooves in the cheeks or irritating the ears, the nasalabidial area, inside the nostrils and under the neck. Further, there is a need for a cannula to fit properly when first removed from the package and reduce the storage space needed to maintain a cannula inventory. There is also a need for cannulas that can be comfortably used in cold temperatures and main supply tubing that does not form twisted loops.